1. Field of the Invention
This invention relates to a pane comprising a substrate of glass, coated with a thin functional film, the latter having properties of transparency, electrical conductivity and/or low emissivity, and having disposed between the substrate and functional film, an intermediate film.
The invention also relates to a method for the production of such a pane, in particular by means of pyrolysis techniques or techniques using vacuum.
2. Description of the Prior Art
Panes coated with films with low emissivity are useful for building construction and ship building. It is known that panes coated with such films have emission in the far infrared, in a direction from the inside to the outside of the room, which is substantially reduced as compared to uncoated panes. By reducing the energy losses resulting partly from this escape of radiation out of the room, the comfort of inhabitants inside the room is substantially improved, especially in winter. If such a film-coated glass substrate is then associated with another substrate through the intermediary of a layer of gas (so that the low-emissivity film is situated on face 3 counting from the outermost face), a very efficient insulating double glazing is formed.
Panes coated with functional films are also useful in applications relating to automobiles because of their electrical conduction properties which make them ideal as, for example, heating panes when provided with electrical supply conductors. Various thin films composed of metal oxide films are known which exhibit these properties, such as films of indium oxide doped with tin (ITO); zinc oxide doped with aluminum (ZnO:Al), indium (Zno:In), tin (ZnO:Sn) or fluorine (ZnO:F); or tin oxide doped with fluorine (SnO.sub.2 :F). For example, films of aluminum oxide, titanium oxide, tin oxide, zinc oxide and indium oxide, are described in French Patent Application FR-A-2 670 199.
These metal oxide films can be produced by various processes including vacuum processes such as thermal evaporation or cathodic sputtering (possibly assisted by magnetron) or by the pyrolysis of organometallic compounds projected by a carrier gas in liquid, solid or gaseous form, onto the surface of a glass substrate which is heated to a high temperature but which nevertheless has not reached its softening point. These organometallic compounds, when brought into contact with a hot glass surface, decompose by oxidizing to form a metallic oxide film on the surface of the glass. The latter technique is especially advantageous because it can be used to deposit a metal oxide film continuously onto a glass ribbon directly from a production line of the float type.
Thin films can also be deposited by processes well known in the art such as by pyrolysis, especially by gaseous process CVD (Chemical Vapor Deposition), as taught in French Patent Application FR-A-2 677 689 or by a plasma-CVD technique, as taught in Patent Application EP-A-413 617.
Thin films composed of metal oxides can also be deposited by powder pyrolysis of organometallic precursors, or alternatively, by liquid pyrolysis of organometallic precursors, as proposed in European Patent Application EP-A-465 309.
Films of tin oxide doped with fluorine have been produced from dibutyl tin oxide (DBTO) in powder form and gaseous anhydrous hydrofluoric acid as described in patent FR-2 380 997, and from dibutyl tin difluoride (DBTF), possibly in a mixture with DBTO, as described in EP-A-178 956 or EP-A-039 256. Films of ITO, have been produced, for instance, from indium formate and a tin compound such as DBTO as described in EP-A-192 009.
Films of SnO.sub.2 :F have also been produced by pyrolysis of compounds in the gaseous phase, preferably from a mixture of tin compounds such as (CH.sub.3).sub.2, SnCl.sub.2, (C.sub.4 H.sub.9).sub.2 SnCl.sub.2, Sn(C.sub.2 H.sub.5).sub.4 and organofluorinated compounds such as CCl.sub.2 F.sub.2, CHCl.sub.2 and CH.sub.3 CHF.sub.2, as described in Patent Application EP-A-027 403, and from monobutyl tin trichloride and a compound of the formula XCHF.sub.2, such as chlorodifluoromethane, as described in Patent Application EP-A-121 459.
Films of SnO.sub.2 :F have also been obtained in the liquid phase from tin acetylacetonate and from dimethyltin-2-propionate in suitable organic solvents, as described in French Patent 2 211 411.
Films of zinc oxide doped with indium or with aluminum have been produced by pyroiysis in the vapor phase from diethylzinc or zinc acetate and triethylindium, indium chloride, triethylaluminium or aluminum chloride, as described in Patent Application EP-A-385 769.
However, in order for any of the above films to function satisfactorily in terms of emissivity and/or electrical conduction, they must have a geometric thickness of at least 180 to 400 nm, and usually must be between 300 and 400 nm. Within the latter range of thicknesses, these films coated panes have a colored reflected appearance on the "film side" which is at a level of light reflection and a color intensity which is aesthetically unpleasing.
For example, according to the teaching of Patent EP-B-0 125 153, when a film of tin oxide doped with fluorine SnO.sub.2 :F having a thickness of approximately 163 to 165 nm, is deposited onto a substrate of clear float glass of 4 mm thickness, the substrate has a reflected color in the blues, a coloration which is much sought after today both in the field of building and in automobile construction. Unfortunately, it has been found that when a film of the same composition but with a thickness of 360 nm, a film which therefore has better performance characteristics, is coated onto the same substrate, the reflected appearance on the film side is slightly purple, a color which is not desirable due to aesthetic reasons.
It is therefore highly desirable to be able to control the reflected appearance of a glass substrate, especially the residual coloration obtained on the "film side" of a film coated substrate.